C++ 代码

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* merge(ListNode* l1, ListNode* l2) {
        if(!l1||!l2){
            return !l1?l2:l1;
        }
        ListNode* dummy=new ListNode(0);

        ListNode*head=dummy;
        while(l1&&l2){
            if(l1->val>l2->val){
                head->next=l2;
                l2=l2->next;
            }else{
                head->next=l1;
                l1=l1->next;
            }
            head=head->next;
        }

        if(l1){
            head->next=l1;
        }
        if(l2){
            head->next=l2;
        }
        return dummy->next;
    }  
};